The optical properties of single crystal hexagonal GaN films grown on (0001) sapphire substrate by metalorganic chemical vapor deposition were investigated. The energy gap of hexagonal GaN was determined as 3.39 and 3.400 eV by optical transmission and photoreflectance, respectively. The refractive index of GaN as a function of photon energy was drawn from the transmission spectrum. Furthermore, Raman scattering spectra were employed to study the phonon modes of the GaN film. The properties of LO phononplasmon coupled modes were further studied, and the carrier concentration and damping constant were determined by line-shape fitting of the coupled modes.